One-way-featured phase transition of confined oxygen (O$_{2}$) in porous materials with different geometry restrictions

The confinement effect of oxygen adsorbed in porous materials (MCM-48, MCM-41 and vycor) has been investigated by means of susceptibility measurements. A one-way-featured phase transition has been found at the phase transition of \textit{$\alpha $}$\to $\textit{$\beta $} on heating in MCM-41 and vycor. Our studies has clearly revealed that the confinement effect of oxygen confined in porous materials is dependent on the geometry restrictions: MCM-48 with ordered three-dimensionally (3-D) interconnected pore systems shows a complete bulk feature of oxygen, whereas MCM-41 with 1-D long nonintersecting arrays and vycor with randomly oriented 3-D connected pores show typical confinement effects of oxygen.